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Unseptpentium
Unseptpentium, Usp, is the temporary name for element 175. NUCLEAR At least one set of theoretical values for half-lives and decay modes of Usp have been constructed for neutron count up to N = 333(1). It predicts isotopes ranging from Usp 454 to Usp 507 in three bands: Usp 454 to Usp 456, Usp 471 to Usp 494, and Usp 504 to Usp 507. Examination of pp 15 & 18 of Ref. 1 indicates that Usp 471 through Usp 494 are part of the expected pattern of alpha-decaying nuclei centered on the N = 308 shell closure. Most have sub-microsecond half-lives, which is also consistent with the pattern of decreasing alpha decay half-lives predicted as Z goes from 115 to 118 in the vicinity of N = 184. Usp 454 to Usp 456 is isolated, very neutron-poor, and not located in the vicinity of any suggested shell closure; it appears to be an artifact of the sort common near the edges of models. Usp 485 to Usp 487 are indicated to have half-lives of at least 1 sec, and may go up to around 1000 sec. That band is also reported to decay by fission. Neutron counts for the isotopes involved are 310 <= N <= 312, which implies alpha decay and a short half life. Those nuclei are more likely to be similar to the other isotopes in their band. What Ref. 1 can’t do is describe heavy isotopes of Usp. It is possible to use a first-order, liquid-drop approach to guess at what lies there. At least two computations of the neutron dripline’s location up to Z = 175 exist(2),(3), and since they give similar results, the maximum possible size of a Usp nucleus can be set slightly above the values computed, allowing only a small margin for error. This gives Usp 626 as the heaviest possible Usp isotope. Similarly, a realistic lower bound can be set by requiring that the amount of energy needed to stabilize a nucleus be no more than twice what is needed to stabilize Usp 471. Within this range, the liquid-drop model can be used to indicate the amount of structural correction energy needed to allow a drop of nuclear matter to survive for the 10^-14 sec needed for electromagnetic interactions (such as binding an electron) to become important. In general, it is not possible to describe structural correction energy. What can be predicted are neutron and proton shell closures, for which correction energy is expected to be particularly large. Neutron shell closures have been predicted at N = 406(3),(4), 370(3), 318(5), and 308(1). The isotope Usp 581 requires 1.5 MeV of structural correction, which means isotopes in the Usp 571 to Usp 586 band are likely. (See “Formation” for additional significance of these nuclei.) Usp 545 requires 2.5 MeV of structural correction, which means isotopes in the band Usp 535 to Usp 550 are also likely. All isotopes in both bands should beta-decay with half-lives under a second. On the other hand, Usp 493 requires 7.5 MeV of correction energy, which means it can only stabilize nuclides if it provides strong correction. Ref. 1 does not show a pattern of nuclides which indicate strong closure at N = 318. Usp 483 requires 9.5 MeV of correction energy, which is realistic for a strong neutron shell closure, such as the one predicted at N = 308, so the liquid-drop picture isn’t unrealistic. ATOMIC Electron structure of Usp has not been studied closely, but it is likely to differ significantly from what's found at lower atomic numbers. It is likely that orbital theory breaks down between Z = 170 and Z = 175. While only the innermost electrons would be qualitatively different, other orbitals would be affected sufficiently to change the ground state occupation. Usp is also large enough that nuclear shape may have an effect on electron structure, which might cause different isotopes of Usp to have different electronic structures. (That means it is no longer an element in the chemical sense.) Predictions of atomic or chemical properties of Usp are risky. FORMATION Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. There is a possibility that beta decay from dripline nuclides stabilized by the N = 406 closure, enhanced by the Z = 164 proton shell closure, will allow some isotopes in the vicinity of Usp 571 to Usp 577 to form in quantity during such a merger. It improbable that nuclides between Usp 535 and Usp 550, or lighter, can form in this way . Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Usp 471 to Usp 494 band. Quantities produced by this method are very small. REFERENCES 1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 2. "Neutron and Proton Drip Lines Using the Modified Bethe-Weizsacker Mass Formula; D.N. Basu et al; Int.J.Mod.Phys.; arXiv:nucl-th/0306061; url: https://arxiv.org/abs/nucl-th/0306061 3. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 4. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 5. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (12-11-19)